↵a One passage represents a 1:500 dilution of a late-exponential-phase culture to 1 × 108 cells/ml to 1 × 105 to 5 × 105 cells/ml after ca. 7 days of growth at 23°C.

↵b Representative clones were chosen on the basis of their differing colony morphologies (Table 1).

↵c Plasmid content was assessed by PCR of individual clones derived from P1.1 and P1.6 clones after the indicated number of passages, as described in Materials and Methods. Plasmids that were not detected by PCR are listed. Dashes indicate that a PCR product was obtained for all plasmids.

↵d NE, nonexistent. Plating of this passage resulted in colonies that all showed morphology F; no colonies with morphology E were obtained.